1. Technical Field
The present invention pertains to a method, a system and a node for filtering signals in a wavelength division multiplexing (WDM) optical communications system, especially for re-configurably adding and dropping signals to and from an optical fiber path.
2. Description of Related Art
Wavelength division multiplexing (WDM) is a method for high bandwidth transmissions in optical fibre communication systems. In WDM, the optical transmission spectrum is divided into a number of separated wavelength bands, where each wavelength supports a single communication channel. Several channels can be transmitted simultaneously on the same optical fibre. WDM can be used for point-to-point communication where two nodes, one in each end of the fibre, are connected, or for multipoint-to-multipoint communication where several nodes share the transmission capacity on one fibre or one pair of fibres. In the case of multipoint-to-multipoint communication the fibre path usually forms a closed loop (a ring) in order to have two different routes in between a certain pair of nodes in the case of fibre or other equipment failure. But bus networks where end nodes are located in different places are also possible. An example of an add-drop node in such a ring or bus WDM network is provided in application EP 0905936 A2.